The present invention relates to a printer, and in particular to an ink jet printer typically used in association with a computer.
A parameter of ink jet printers is the spacing (i.e., distance) between the printhead and the platen upon which the print media advances. A typical spacing between the printhead and the platen is 1.20 mm. This spacing must be constant, within a tolerance of, for example, +/xe2x88x920.15 mm, along the entire printing path of the printhead to obtain uniform printing. For large format printers, it is a challenge to maintain the spacing between the printhead and the platen within a tolerance of +/xe2x88x920.15 mm or less because a typical length of the printing path is 1.5 m or larger.
A conventional printer includes a carriage that supports the printhead above the platen. The carriage moves laterally along one or two steel rods. In the past, practitioners formed the rods to be as straight as possible in order to maintain the amount of variation in the printhead to platen spacing within a specified range along the printing path.
Another solution is described in U.S. Pat. No. 5,195,836. The ""836 patent discloses a guideway and support structure for a carriage. The guideway includes two rods. The rods are not necessarily pre-straightened, but rather are bent straight to the required tolerance as the rods are attached to and held by the support structure.
An ENDCAD printer employs a different approach. The ENDCAD printer comprises carriage that moves on a single rod. Equally spaced along the rod are two adjustment screws that are perpendicular to the rod. The opposing ends of each screw are threaded. The two threads of each screw are the same pitch. The upper end of each screw engages a hole in the lower part of the rod. The opposite lower end of each screw engages a hole in an chassis member located beneath the rod. Rotating a screw moves the rod a distance equal to two times the thread pitch, since there are two equal threads on the screw. Neither of the two screws are differential screws.
Embodiments of the present invention allow for greatly reducing the amount of variation in the spacing between a printhead and a platen along the length of a printing path of a printer. In particular, the present invention allows very precise adjustments of the printhead to platen spacing. Prior art solutions, including the ENDCAD system described above, do not allow the easy and fine adjustments enabled herein.
One embodiment of the present invention includes a printer having a printhead, a platen spaced from the printhead, and a carriage that moves the printhead laterally adjacent to the platen. The carriage travels on a pair of rods supported by a beam. One or more adjustment assemblies are located beneath and along the length of the beam. Each adjustment assembly applies selected amounts of bending force to the lower side of the beam, and thereby raises or lowers the beam and the rods relative to the platen at that point. Accordingly, there is a corresponding change in the printhead to platen spacing at that point. The printhead to platen spacing along the length of the printing path may be maintained within a specified range by appropriate adjustment of each of the adjustment assemblies.
In one embodiment, each adjustment assembly includes a U-shaped member having a central plate that abuts the lower surface of the beam. The adjustment assembly also includes a first adjustment co-located with a second adjustment. The first adjustment is an acorn nut having a rounded surface that abuts the central plate of the U-shaped member, and the second adjustment is a differential screw that is engaged with the acorn nut. The differential screw has two threads of a different pitch. One thread is engaged with the acorn nut, and the other thread is engaged with a base plate of the adjustment assembly. The amount of adjustment caused by rotation of the differential screw is the difference between the pitch of the two threads. The acorn nut and the differential screw have a common vertical axis that is aligned with a centroid of the beam, which allows the application of vertical force to the beam without the introduction of rotational forces.
These and other objects, features and advantages of the present invention will be more readily apparent from the figures and the detailed description of the exemplary embodiments set forth below.